Purpose and Program Characteristics: The goal of this training program is to prepare scientists for careers as independent investigators of the molecular and cellular mechanisms of host defense. Training in this area is fundamental to continuing evolution of new molecular strategies to ameliorate or prevent diseases of autoimmunity, cancer and congenital and acquired immunodeficiency, as well as problems associated with bone marrow and solid organ transplantation. The trainees include predoctoral and M.D. and Ph.D. postdoctoral fellows. The faculty of the training program include fourteen M.D. or Ph.D. investigators with primary or joint appointments in the Immunology Section of the Department of Microbiology and Immunology at Baylor College of Medicine. The research programs of these faculty address diverse areas of modern immunology, including lymphoid development, antigen receptor gene expression, antigen structure, peptide-MHC interaction, lymphocyte activation and regulation, adhesion molecules in leukocyte trafficking and effector function, mucosal immune response, the neuroendocrine/immune system intersect, and lymphocyte function in HIV infection. Trainees: Support for four predoctoral and three postdoctoral trainees is requested. Predoctoral trainees will be selected from students who have matriculated in the graduate program of the Department of Microbiology and Immunology and have selected one of the training faculty as their thesis mentor. A core curriculum in basic and advanced areas of immunology and in modern cell and molecular biology will be completed by these trainees. Postdoctoral trainees will be selected from highly qualified Ph.D. and M.D. applicants to individual training faculty. M.D. trainees will also be recruited from M.D. fellows in the Allergy and Immunology or Rheumatology subspecialty training programs of the Departments of Medicine and of Pediatrics. Advanced immunology courses and selected molecular biology training, and advisory oversight of research training and career development will be provided to post doctoral trainees. Training Facilities and Environment: Modern research facilities are located in approximately 30,500 sq. ft. in individual investigator laboratories in recently expanded departmental spaces in the DeBakey, Cullen, and Smith buildings of the central Baylor complex and in research facilities of the adjacent Methodist, Texas Childrens and Houston VA Medical Center hospitals. The Graduate School provides important administrative, financial and recruiting support to the program and soon additional physical space in a new Graduate Education Center. The proposed training will occur in the context of the research environment of Baylor College of Medicine, highly ranked among medical schools nationwide in NIH extramural research awards, and of the Texas Medical Center which contains forty research and clinical training institutions and is the largest medical center in the world.